An emergency meeting of international health experts has begun in Geneva to discuss fears that crisps, chips and certain types of bread may cause cancer.

If what we know from water and animal experiments is true, it could be a very significant source of cancer in humans

Dr Jorgen Schlundt, WHO co-ordinator

The World Health Organisation (WHO) has called the three-day meeting of 25 experts following the publication of a Swedish survey in April which showed that some starch-based foods contained the chemical acrylamide, which is thought to be linked to cancer.

Researchers from Stockholm University and Sweden's National Food Administration found acrylamide was formed when carbohydrate-rich foods such as potatoes, rice or cereals were heated.

The study said that an ordinary bag of crisps may contain up to 500 times more of the substance than the top level allowed in drinking water by the (WHO).

"Since then, the United Kingdom and Norwegian National Food Agencies have also published similar findings," the WHO said in a statement.

"The limited data available at this moment does not, however, present us with a full picture, neither of the formation of acrylamide in food or of the consequences to human health," the statement said.

Tests on rats

Acrylamide is a substance used to produce plastics and to purify water and it is known to be carcinogenic.

The WHO says people should eat more fruits and vegetables

Scientists have long warned about the possible harmful effect on humans who are exposed to the chemical in drinking water or in certain occupations.

But the study showed that the chemical is also found in high carbohydrate foods like bread and potato products which are common in many people's diets.

Tests on rats in Sweden showed that when deep fried potato and starchy foods cooked at high temperatures were fed to the animals, many of them developed cancer.

Acrylamide induces gene mutations and has been found in animal tests to cause benign and malignant stomach tumours.

It is also known to cause damage to the central and peripheral nervous system.

'Early stages'

So far there is no proof that the foods would have the same harmful effects on humans.

But the findings have startled the WHO which, together with the United Nations Food and Agriculture Organisation, wants to determine the full extent of the risk to public health.

The meeting behind closed doors will address key issues such as whether acrylamide can be taken up from food as readily as it can from water and whether this uptake could lead to cancer.

"If what we know from water and animal experiments is true, it could be a very significant source of cancer in humans," Dr Jorgen Schlundt, co-ordinator of the WHO's food safety programme said.

"We are still very much at the first stage of the investigation."

The WHO said its basic dietary advice had not yet changed.

It said that people should continue to eat more fruit and vegetables and should cut back on fatty and fried foods.